1. Field of the Invention
The present invention relates to a fuel injector for an internal combustion engine and, particularly, to a fuel injector for an internal combustion engine in which the injection hole is formed in the shape of a slit to produce the spray of a flat fan shape.
2. Description of the Prior Art
In a fuel injector for supplying fuel to an internal combustion engine, the injection hole is formed in the shape of a slit to produce a spray of the shape of a flat fan. Japanese Unexamined Patent Publication (Kokai) No. 3-78562 discloses such a fuel injector for an internal combustion engine. The spray of the shape of a flat fan formed by the fuel injected from the slit-like injection hole of this fuel injector has a small dispersion in concentration and a greatly increased surface area of the spray compared with that of the spray of an ordinary conical shape, enabling nearly all of the fuel to come into sufficient contact with the air and, hence, to be quickly atomized and mixed. This makes it possible to supply, to the internal combustion engine, a fuel spray having a small dispersion in the concentration and in which the fuel is sufficiently atomized.
There, however, remains a problem in that with the slit-like injection hole, it is not easy to adjust the flow rate of the fuel and it is difficult that the flat fan shape of the spray corresponds precisely to the shape of the slit-like injection hole. The flow rate of the fuel varies depending upon the minimum sectional area of the injection hole. In order to set the flow rate of the fuel to a desired value, the minimum sectional area of the injection hole must be correctly set. In the case that the fan-shaped slit-like injection hole is formed to communicate with a general fuel reservoir having a hemispherical shape, the area of the communication portion between the injection hole and the fuel reservoir is the minimum sectional area of the injection hole, if geometrically simplified, the area can be considered to be the area of the region where a curved surface meets a quadrangular pyramid. Therefore, a small change in the position of the slit-like injection hole causes a change in the sectional area of the communication portion that is opened to the fuel reservoir, i.e., a change of the minimum sectional area of the injection hole, making it difficult to obtain a desired amount of injected fuel. In the slit-like injection hole that produces the spray of the shape of a flat fan, furthermore, the flow of the fuel easily becomes nonuniform. Particularly, it is difficult that the fuel flows in the side regions of the injection hole in the flattened direction as same as in the central region thereof due to the wall resistance of the injection hole, the included angle of the spray of the fan shape tends to become smaller than the included angle of the injection hole of the fan shape, and the spray becomes thin in the side regions of the spray in the flattened direction.